On the assumption that mechanical factors in diarthrodial joints may contribute to the pathogenesis of osteoarthritis, an experimental ultrasonic technique has been developed to measure, in vitro, the global and detailed geometry of the unloaded acetabula, establishing the sphericity and aberrations of the cartilage surface and calcified subchondral bone. A second ultrasonic technique provides direct measurement of cartilage consolidation under load, over the global coordinates of the acetablum. With a pressure-instrumented prosthesis, the overall pressure distribution can also be determined and compared with the geometrical features. An in vivo pressure-instrumented prosthesis contained within an otherwise standard femoral head replacement (Moore) prosthesis has been developed. It transmits PAM/FM telemetry of the instantaneous pressures on fourteen discrete locations on the load-bearing surface and will be implanted in consenting humans who require this surgical reconstruction. The in vivo distribution data will be compared with the more comprehensive in vitro data, which are assembled from a wide-range of autopsy specimens, including healthy and diseased, various ages, etc. Data from the in vivo prosthesis in combination with estimates of the force across the human hip joint derived from calculations based on kinematic variables will permit partitioning the multiple muscle forces across the hip joint between those stabilizing the joint and those contributing to joint movement.